There has been conventionally employed a film carrier method for mounting a semiconductor element, wherein a metal protrusion for connection purposes (hereinafter this protrusion is referred to as a bump) is used for the inner bonding between a lead on a film carrier and an electrode of a semiconductor element.
When the above-mentioned bump is formed on an electrode of a semiconductor element, however, a metal layer of titanium, chromium and the like for adhesion, and a metal layer of copper, platinum, palladium and the like as a barrier for preventing diffusion of bump metal are formed on the electrode surface by sputter-etching, evaporation and the like, on which a bump of gold and the like is formed, thus making the process extremely complicated. Moreover, there is a likelihood that the semiconductor element and/or electrode surface may be contaminated or damaged during the process of forming a bump on the electrode surface.
A method has been proposed which uses an anisotropic conductive film having conductivity in the thickness direction of a film, for bonding without forming a bump on an electrode surface. Specifically, that wherein conductive particles of carbon black, graphite, nickel, copper, silver and the like are oriented in the direction of thickness of an insulating film and dispersed therein. When the orientation of the dispersed conductive particles is insufficient, however, an electric connection between the electrode of semiconductor element and a lead of film carrier becomes uncertain, thus posing problems in terms of connection reliability.
On the other hand, a method comprising forming a bump on the lead side of film carrier and directly connecting the bump to an electrode of semiconductor element. When wiring of semiconductor element is fine-pitched or highly dense, however, this method is faced with a difficulty in forming a circuit and/or bump corresponding to such semiconductor element on a film carrier, and also requires much attention during connecting operation.
When a conventional film carrier having a wire circuit and/or a bump set on an insulating film surface is used, moreover, outer lead bonding area generally becomes greater than inner lead bonding area, so that the final mounting area becomes greater than the size (area) of the semiconductor element, which in turn makes it difficult to satisfy a possible future demand for miniaturization.
A semiconductor element after mounting is often protected by sealing the entirety of the semiconductor element. A conventional film carrier has an exposed conductive circuit, so that an insulating resin to be used for sealing comes into direct contact with the conductive circuit. Inasmuch as the insulating resin and the metallic material forming the conductive circuit show low adhesion property, water in the air and the like penetrates into the interface thereof to possibly degrade the reliability of the semiconductor device.